Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Disk Technology

The discussion of hardware architectures in this chapter so far has centered on ways of increasing performance by increasing system resources such as CPUs, memory, and I/O subsystems and on the resulting parallelism that can take advantage of these resources.

Another way to increase performance by adjusting hardware is to tune for I/O, which includes tuning for disk layout. Since disk access has the greatest latency, the major focus of I/O tuning should initially be on keeping what has been retrieved from disk in memory. The actual performance of retrieving that data from disks can also be improved by spreading the data evenly across multiple disks and by making sure there are enough disk controllers to transfer the data from disk onto the I/O bus and into memory.

Usually, disk performance issues can be identified on systems with sluggish performance but relatively low CPU utilization. You can use tools such as the Oracle Enterprise Manager Tuning Pack to identify where the bottlenecks are.

Disk Controllers

The slowest but most common disk controller used today is the Small Computer Systems Interface (SCSI). The name comes from the fact that these controllers were initially intended for PCs. Over the years and through several generations of SCSI controllers performance has improved, and the controllers now appear in the largest MPP and SMP systems with faster variations such as “fast and wide SCSI” and “Ultra SCSI.” The benefit of using SCSI disk devices is that ...